Double acting cold trap

ABSTRACT

A double acting cold trap equipped with a set of exhaust gas condensing fins and a set of exhaust gas condensing plates is disclosed. The invention also discloses a double acting cold trap that incorporates a deflecting plate to direct the exhaust gases over the condensing fins and plates in a serial fashion. This increases the efficiency of the collection of unwanted particles.

BACKGROUND OF THE INVENTION

[0001] (1) Technical Field

[0002] This invention relates generally to an apparatus used in asemiconductor manufacturing process for effectively collecting unwantedby-products in the exhaust gases of a low pressure chemical vapordeposition film fabrication process.

[0003] (2) Description of Prior Art

[0004] The following four U.S. Patents relate to cold traps for reducingsource material from a reaction chamber.

[0005] U.S. Pat. No. 6,24,793b1 issued Jun. 5, 2001, to Jui-Hsiung Leeet al. disclosing a cold trap with a curvilinear cooling plate.

[0006] U.S. Pat. No. 6,107,198 issued Aug. 22, 2000, to Wei-Farn Lindiscloses an apparatus and method for reducing process solid buildup byusing an exhaust circuit of cold traps and heating

[0007] Another objective of the present invention is to provide a coldtrap with increased cooled surface area for the deposition of unwantedparticles.

[0008] An additional objective of the present invention is to provide agas deflecting plate that directs the gas over a second set of coolingfins to allow for a larger area for deposition of unwanted particles.

[0009] A further objective of the invention is to provide a second setof cooling fins so shaped as to provide additional cold surface area fordeposition of unwanted particles.

[0010] It is also the objective of the invention to provide cooling finsso shaped as to minimize the impedance to gas flow.

[0011] The above objectives are achieved by the present invention byproviding a double acting cold trap that incorporates a cylindricalhousing with exhaust gas inlet and outlet ports arranged at 90°.Internal to the cylindrical housing are a set of condensing fins and aset of condensing plates. A deflecting plate is incorporated between thecondensing fins and condensing plates that directs the exhaust gases ina serial fashion over the condensing surfaces. Input and output fittingsfor the cooling fluid are incorporated on the stainless steel housingand the fluid loop is so arranged as to provide fluid to the condensingfins and condensing plates in a closed circulating loop.

DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic of a LPCVD system of the prior art.

[0013]FIG. 2 is a cross sectional view of a cold trap of the prior art.

[0014]FIGS. 3a, 3 b, 3 c are cross sectional views of the double actingcold trap as described in this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] Silicon nitride films are widely used in semiconductor waferprocessing. A LPCVD system is the preferred method for depositing thesilicon nitride film. During the chemical reactions of the processunwanted particles such as ammonium chloride powder are formed in thereaction chamber. In order to minimize the deleterious effects of thesecontaminants, increased defect density on the product, and increasedcleaning frequency of LPCVD system, a cold trap is incorporated in thesystem. FIG. 1 unit 11.

[0016] The present invention discloses a double acting cold trap forcollecting the unwanted particles such as ammonium chloride, asdescribed above.

[0017] In the present invention double acting cold trap, a cylindricalhousing is used to support a deflecting plate and two sets of coolingfins. The housing also contains a gas inlet port on the cylindricalsurface of the housing and a gas outlet port perpendicular to the gasinlet port. The housing also incorporates a sealing plate on theopposite end of the gas outlet port that provides inlet and outletconnections for the cooling water that flows through the cooling fins.

[0018]FIG. 3a is a cross section of the double acting cold trap, thepresent invention. The double acting cold trap is constructed using acylindrical housing 20. The housing 20 is provided with a gas inlet port22, and a gas outlet port 24 perpendicular to the gas inlet port 22.

[0019] Internal to the cylindrical housing 20 is mounted a gasdeflecting plate 26 which directs the exhaust gases over the sequencedcold condensing plates. Mounted on the opposite end of the gas outlet isa plate 28 which supports the cooling water inlet 30 and the coolingwater outlet 32. The cooling water piping inlet and outlet are sodesigned as to support and provide cooling water to the first pluralityof cooling fins 34 parallel to the exhaust gas flow, and to support andprovide cooling water to the plurality of cooling plates 36perpendicular to the exhaust gas flow.

[0020]FIG. 3b is a bottom view of the double acting cold trap showingthe configuration of the two sets of condensing cold plates 38, 40. Item38 of FIG. 3b is the first exhaust gas condensing cold plate whichincorporates a set of cooling fins 34 which provides a large area forcondensation and collection of unwanted particles. Item 40 of FIG. 3b isthe second exhaust gas condensing cold plate which incorporates a seriesof cooling plates with holes to allow the flow of gas. These coolingplates provide additional area for condensation and collection ofunwanted particles. FIG. 3c is a plan view with the housing removed ofthe first set of cooling fins item 38.

[0021] In the arrangement of the present invention as shown in FIG. 3a,the plurality of condensing cold plate fins and plates 34, 36 exposed tothe exhaust gases has been shown to result in lower defect densities onthe product and longer periods between required major preventivemaintenance.

[0022] Although the invention has been described and illustrated withreference to specific illustrative embodiments thereof, it is notintended that the invention be limited to those illustrativeembodiments. Those skilled in the art will recognize that variations andmodifications can be made without departing from the spirit of theinvention. It is therefore intended to include within the invention allsuch variations and modifications which fall within the scope of theappended claims and equivalents thereof.

What is claimed is:
 1. A double acting cold trap for collecting unwantedbyproducts, reactants and particles in the exhaust gases of a lowpressure chemical vapor deposition system comprising: A cylindricalstainless steel housing; A gas inlet port on the side of the cylindricalsteel housing; A gas outlet port on the bottom of the cylinder; and Agas condensing apparatus with cooling liquid inlet and outlet fittings,condensing fins parallel, and plates perpendicular to the gas flow. 2.The double acting cold trap of claim 1, wherein the condensing fins andplates are so arranged as to allow the exhaust gases to first pass overthe condensing fins and secondly over the condensing plates.
 3. A doubleacting cold trap with condensing fins and plates so arranged as tomaximize the condensing surface area presented to the exhaust gases. 4.The double acting cold trap of claim 1 wherein said condensing fins andplates are so arranged as to utilize the same cooling liquid input andoutput fittings.
 5. The double acting cold trap of claim 1 furthercomprising a deflecting plate that directs the exhaust gas flow over thecondensing fins and secondly over the condensing plates, in a serialfashion.
 6. The double acting cold trap of claim 1 wherein said platesincorporate holes so arranged as to allow for free flow of exhaustgases.
 7. The double acting cold trap of claim 6 wherein said plateswith holes that are staggered plate to plate so as to maximize thesurface area of the condensing plates in contact with the exhaust gases.8. The double acting cold trap of claim 1 wherein said gas inlet andoutlet ports arc arranged at 90° so as to allow for a double set ofcondensing fins and plates to be arranged in the exhaust gas path. 9.The double acting cold trap of claim 1 wherein said exhaust gas inletand outlet ports are arranged at 90° to provide for integration to theoverall LPCVD system.
 10. The double acting cold plate of claim 6wherein said hollow condensing fins and plates provide a closed circuitpath for the cooling fluid.
 11. A method of collecting unwantedby-products, reactants and particles in exhaust gases of a low pressureCVD system comprising the steps of: Providing a cylindrical steelhousing; Providing a gas inlet port on a side of the cylindrical steelhousing; Providing a gas outlet port on the bottom of the cylindricalsteel housing; Providing a gas condensing apparatus with cooling liquidinlet and outlet fittings, condensing fins parallel, and platesperpendicular to the gas flow. And flowing said exhaust gases over saidfins and plates.
 12. The method of claim 11 by the use of a doubleacting cold trap utilizing said condensing fins and plates, wherein saidcondensing fins and plates are so arranged as to allow the exhaust gasesto first pass over the condensing fins and secondly over the condensingplates.
 13. The method of claim 12 wherein said double acting cold traputilizes said condensing fins and plates so arranged as to maximize thecondensing surface area presented to the exhaust gases.
 14. The methodof claim 12 wherein said condensing fins and condensing plates areconnected and arranged to allow for the utilization of common liquidinput and output fittings.
 15. The method of claim 11 wherein adeflecting plate is utilized that directs the exhaust gases over thecondensing fins; and secondly, over the condensing plates of an LPCVDcold trap.
 16. The method of claim 11, further comprising arrangingholes in the condensing plates so as to minimize resistance to the flowof exhaust gases while maximizing the surface area of the condensingplates in contact with the exhaust gases.